The invention relates to nucleotide sequences and proteins for anti-pathogenic agents and their uses, particularly the genetic manipulation of plant with genes that enhance disease resistance. Promoter sequences are also provided.
Plant diseases are often a serious limitation on agricultural productivity and have therefore influenced the history and development of agricultural practices. Only recently have Mendelian genes controlling disease resistance been isolated, and elucidation of their biochemical functions remains a major challenge.
Plant disease outbreaks have resulted in catastrophic crop failures that have triggered famines and caused major social change. Generally, the best strategy for plant disease control is to use resistant cultivars selected or developed by plant breeders for this purpose. However, the potential for serious crop disease epidemics persists today, as evidenced by outbreaks of the Victoria blight of oats and southern corn leaf blight.
Mendelian genetics of resistance to disease in plants is well known. Resistance is often controlled by a single gene, either dominant, semidominant, or recessive. In some instances, multigenes are involved. However, the biochemical mechanisms for gene products involved in plant resistance are known in only a few model cases.
Among the causal agents of infectious diseases of crop plants, phytopathogenic fungi play the dominant role not only by causing devastating epidemics, but also through the less spectacular although persistent and significant annual crop yield losses that have made fungal pathogens a serious economic factor. All of the species of flowering plants are attacked by pathogenic fungi. Generally, however, a single plant species can be host to only a few fungal species, and similarly, most fungi have a limited host range.
To colonize plants, fungal microorganisms have evolved strategies to invade plant tissue, to optimize growth in the plant, and to propagate. Bacteria and viruses, as well as some opportunistic fungal parasites, often depend on natural openings or wounds for invasion. In contrast, many true phytopathogenic fungi have evolved mechanisms to actively traverse the plant""s outer structural barriers, the cuticle and the epidermal cell wall. To gain entrance, fungi generally secrete a cocktail of hydrolytic enzymes.
Despite the large number of microorganisms capable of causing disease, most plants are resistant to any given pathogen. The defense mechanisms utilized by plants can take many different forms, ranging from passive mechanical or preformed chemical barriers, which provide non-specific protection against a wide range of organisms, to move more active host-specific responses that provide host-or varietal-specific These genes have been employed in breeding programs upon discovery.
A hypersensitive response (HR) that is elaborated in response to invasion by all classes of pathogens is the most common feature associated with active host resistance. In most cases, activation of the HR leads to the death of cells at the infection site, which results in the restriction of the pathogen to small areas immediately surrounding the initially infected cells. At the whole plant level, the HR is manifested as small necrotic lesions. The number of cells affected by the HR is only a small fraction of the total in the plant, so this response obviously contributes to the survival of plants undergoing pathogen attack.
In plants, robust defense responses to invading phytopathogens often conform to a gene-for-gene relationship. Resistance to a pathogen is only observed when the pathogen carries a specific avirulence (avr) gene and the plant carries a corresponding resistance (R) gene. Because avr-R gene-for-gene relationships are observed in many plant-pathogens systems and are accompanied by a characteristic set of defense responses, a common molecular mechanism avr-R gene mediated resistance has been postulated. Thus, disease resistance results from the expression of a resistance gene in the plant and a corresponding avirulence gene in the pathogen and is often associated with the rapid, localized cell death of the hypersensitive response. R genes that respond to specific bacteria, fungal, or viral pathogens have been isolated from a variety of plant species and several appear to encode cytoplasmic proteins. It has been unclear how such proteins could recognize an extracellular pathogen. Many strategies for plant disease control have been attempted. Resistant cultivars has been selected or developed by plant breeders for disease control. Resistance is especially important for major crops such as the cereals, sugar cane, potato, and soybean. The limitation in use of disease resistance in modern agriculture is adaptability by pathogens to overcome resistance.
The development of new strategies to control diseases is the primary purpose of research on plant/pathogen interactions. These include, for example, the identification of essential pathogen virulence factors and the development of means to block them, or the transfer of resistance genes into crop plants from unrelated species. An additional benefit is a better understanding of the physiology of the healthy plant through a study of the metabolic disturbances caused by plant pathogens.
Anti-pathogenic compositions and methods for their use are provided. The compositions comprise anti-pathogenic proteins and their corresponding genes and regulatory regions. Particularly, sunflower PR5-1, defensin, and berberine bridge enzyme (BBE) homologues, and fragments and variants thereof, are provided.
The compositions are useful in protecting a plant from invading pathogenic organisms. One method involves stably transforming a plant with a nucleotide sequence of the invention to engineer broad spectrum disease resistance in the plant. The nucleotide sequences will be expressed from a promoter capable of driving expression of a gene in a plant cell. A second method involves controlling plant pathogens by applying an effective amount of an anti-pathogenic protein or composition of the invention to the environment of the pathogens. Additionally, the nucleotide sequences of the invention are useful as genetic markers in disease resistance breeding programs.
Promoters of the genes of the invention find use as disease or pathogen-inducible promoters. Such promoters may be used to express other coding regions, particularly other anti-pathogenic genes, including disease and insect resistance genes.
The compositions of the invention additionally find use in agricultural and pharmaceutical compositions as antifungal and antimicrobial agents. For agricultural purposes, the compositions may be used in sprays for control of plant disease. As pharmaceutical compositions, the agents are useful for antibacterial and antimicrobial treatments.
The methods of the invention find use in controlling pests, including fungal pathogens, viruses, nematodes, insects, and the like. Transformed plants, plant cells, plant tissues, and seeds, as well as methods for making such transformed compositions are additionally provided.